1. Field of the Invention
The present invention relates to the art of papermaking and more particularly, to techniques for quantitatively monitoring the web characteristic of abrasiveness.
2. Description of the Prior Art
There are many paper converting operations having a high degree of sensitivity to the abrasive characteristic of paper. For example, decorative laminates made with multiple layers of phenolic impregnated kraft paper are machined to final shape with steel cutting tools which may be rapidly dulled. Another example is corrugating medium which abrades away the flutes of corrugating rolls in the primary manufacturing step of corrugated board.
These, and other manufacturing difficulties arising from paper abrasiveness are noted in detail by the publications of George E. Power found in TAPPI Vol. 57, No. 2, February, 1974 at page 95 and Forest Products Journal Vol. 24, No. 1, January, 1974 at page 40.
The abrasive characteristic of paper is due to the silica content thereof. Such silica originates as sand, grit and clay contaminates combined with the raw wood furnish from which the paper pulp is made. The caustic wood digestion process has little or no effect on the contaminates and once combined in the pulp flow stream are extremely difficult to remove. By additional processing such as multiple passes through centrifugal cleaners, such silica content may be significantly reduced. However, it would be prohibitive to process all the pulp produced by a typical two hundred and fifty ton per day pulp mill through cascades of centrifugal cleaners. Moreover, in any given pulp mill, an excessive presence of silica recurs only sporadically. Consequently, tests have been developed by the trade to quantify the abrasive result of silica contained in paper.
The most widely accepted paper abrasiveness test was developed by The Institute Of Paper Chemistry in Appleton, Wisconsin and reported in a paper of restricted dissemination for Project 2696-18 dated Oct. 5, 1976. Basically, this test involves the use of accurately weighed metal foil specimens (brass and steel) attached to the surface of a rotationally fixed cylinder. Over this foil clad cylinder at an approximately 170.degree. wrap angle is drawn a two thousand foot length of twelve inch wide paper web sample. Such drawing is performed at a carefully controlled tensile force. Upon traverse of the sample length, the foil specimen is removed and weighed again for determination of material loss. The magnitude of such weight loss is directly attributed to the abrasiveness of the paper sample.
Although the results of this abrasiveness test are widely accepted as accurate and reliable, it will be noted that elaborate laboratory fixtures are required for an off-machine test having the inherent disadvantage of long delay times between the moment of web issue from the production machine and identification of a characteristic which ultimately relates back to the pulp from which the paper web was laid.
To rectify or at least reduce this informational hiatus, what is needed by the industry is an on-line test of the paper web as it is being formed to determine immediately if the abrasive quality of the paper so produced is increasing so that timely corrective measures may be taken.
It is therefore, an object of the present invention to teach a test procedure for determination of abrasive quality and an apparatus for conveniently performing such a test quickly while the web is still within the papermachine.